The openings for non-cooled oxyburners comprise most often a straight cylindrical passage, as described in U.S. Pat. No. 5,267,850 or comprise a flared outlet region, as described in U.S. Pat. No. 5,092,760. In the first case, the combustion taking place in the passage, the speed of the gases leaving the passage and entering the furnace is very high, even in the case in which the speeds of ejection of the combustible agent and of the oxygenated combustible agent are low, which is inconvenient for numerous uses, in particular in glass furnaces. In the second case, the speeds of ejection must be relatively high to cool the passage of the opening and to avoid the return of combustion gases from the furnace into this latter, which also gives rise to excessive outlet speeds.